(1) Field of the Invention
This invention relates to mechanisms for locking a rotatable load to a drive hub and for unlocking the load such that it may be readily removed when the drive hub is at rest. The invention is particularly, but not exclusively, suitable for use in magnetic tape transports in which the rotatable load is a reel of magnetic tape.
(2) Description of the Related Art
Many designs of magnetic tape transport have been provided with a supply reel drive hub including a number of retractable friction pads which, in a locked position, are spring loaded against the inner cylindrical surface of the supply reel and which may be retracted towards the hub centre to permit loading and unloading of the supply reel. U.S. Pat. No. 4,243,186, for example, discloses a supply reel hub in which the differential rotation of a pair of concentric rotors is used to operate the locking and retracting mechanism for three spring loaded friction pads and in which the mechanism may be automatically operated utilising the power of the supply hub drive motor. While such arrangements are satisfactory for many applications, they suffer from the disadvantage that, in the locked position, the driving torque for each friction pad is proportional to the applied spring pressure, and the spring pressure may vary from one friction pad to another. Such variation may result in the locking mechanism becoming only partially effective and unsuitable for use with high speed tape drives which are required to withstand high rotational accelerations and decelerations, such as intermittent motion fast start-stop digital tape handlers.